Why a Negative x Negative = Positive

Date: 4/11/96 at 16:57:21
From: Anonymous
Subject: proofs, multiplying integers
A teacher in a course I took last fall challenged us to come up
with a way to demonstrate or prove how it is that a negative times
a negative equals a positive (how to explain this). The only
thing I could come up with is that it is positive because one is
negating a negative. No one came up with a very satisfying
explanation. Can you help? Thanks.

Date: 4/18/96 at 13:26:36
From: Anonymous
Subject: Math equations
Hello. I am a student at The Colorado Institute of Art and have
had a question/problem presented to me by our Gen ED math
instructor. The question is:
Are there any other forms of proof to show that (- + - = +)
Negative plus a negative equals a positive?
I have done more researching than one brain could handle, and I
was hoping that with several brains together the answer could be
completed.
I would greatly appreciate your help in any way.
Thank you very much.
Julia